The present invention is drawn toward a reconfigurable plasma antenna for radiating and receiving electromagnetic signal, methods for generating a plasma antenna, and a method for altering the radiation pattern of a plasma antenna. The device includes an enclosed chamber containing a composition capable of forming a plasma, at least three energizing points in electromagnetic contact with the composition, an energy source in electromagnetic contact with the energizing points for energizing the composition and selectively forming one or more conductive paths of plasma within the enclosed chamber, and preferably, a modifying mechanism to reconfigure the conductive path.
Traditionally, antennas have been defined as metallic devices for radiating or receiving radio waves. Therefore, the paradigm for antenna design has traditionally been focused on antenna geometry, physical dimensions, material selection, electrical coupling configurations, multi-array design, and/or electromagnetic waveform characteristics such as transmission wavelength, transmission efficiency, transmission waveform reflection, etc. As such, technology has advanced to provide many unique antenna designs for applications ranging from general broadcast of RF signals to weapon systems of a highly complex nature.
Generally, an antenna is a conducting wire which is sized to emit radiation at one or more selected frequencies. To maximize effective radiation of such energy, the antenna is adjusted in length to correspond to a resonating multiplier of the wavelength of frequency to be transmitted. Accordingly, typical antenna configurations will be represented by quarter, half, and full wavelengths of the desired frequency.
Efficient transfer of RF energy is achieved when the maximum amount of signal strength sent to the antenna is expended into the propagated wave, and not wasted in antenna reflection. This efficient transfer occurs when the antenna is an appreciable fraction of transmitted frequency wavelength. The antenna will then resonate with RF radiation at some multiple of the length of the antenna. Due to this, metal antennas are somewhat limited in breadth as to the frequency bands that they may radiate or receive.
Recently, there has been interest in the use of plasmas as the conductor for antennas, as opposed to the use of metals. This interest is due in part to the fact that plasma antennas can be designed to be more flexible in use than traditional metal antennas. For example, radiated signal from a plasma antenna can be controlled by a number of factors including plasma density, tube geometry, gas type, applied magnetic field, and applied current. This concept has been described in U.S. Pat. No. 5,963,169 which is incorporated herein by reference. In that patent, a plasma antenna is disclosed that is electronically steerable and dynamically reconfigurable. This steerability and reconfigurability allows the antenna to be more efficient and operate in a wider band of frequencies.
Other exemplary art has been disclosed in U.S. Pat. Nos. 3,404,403 and 3,719,829 where the use of a plasma column formed in air by laser radiation as the antenna transmission element is disclosed. Additionally, U.S. Pat. No. 3,914,766 discloses a pulsating plasma antenna which has a cylindrical plasma column and a pair of field exciter members parallel to the column. The location and shape of the exciters, the cylindrical configuration, and the natural resonant frequency of the plasma column all provide enhancement of the natural resonant frequency of the plasma column and energy transfer. Additionally, these factors act to stabilize the motion of the plasma, preventing unwanted oscillations and unwanted plasma waves from destroying the plasma confinement.
U.S. Pat. Nos. 5,594,456 and 5,990,837, both of which are incorporated herein by reference, disclose an antenna device for transmitting a short pulse duration signal of predetermined radio frequency. The antenna device includes a gas filled tube, a voltage source for developing an electrically conductive path along a length of the tube which corresponds to a resonant wavelength multiple of the predetermined radio frequency, and a signal transmission source coupled to the tube which supplies the radio frequency signal. One application of this antenna design is to transmit short pulse duration signal in a manner that eliminates a trailing antenna resonance signal.
Due to the dynamic reconfigurability of plasma antennas, some limitations previously known to exist with metal antennas are beginning to be removed. However, in order to more fully tap into the reconfigurability of plasma antennas, it would be useful to provide a plasma antenna having three or more energizing points that is reconfigurable with respect to signal rate, location of feeds, types of feeds, timing of signal, quantity of feeds energized, intensity of signal, shape of enclosure, density of plasma, and type of composition used.
It is an object of the present invention to provide a plasma antenna that may be controlled by at least three energizing points in electromagnetic contact with a composition capable of forming a plasma to selectively ionize the composition, or portions thereof, within the enclosed chamber.
It is another object of the invention to provide a reconfigurable plasma antenna wherein the radiation pattern may be altered by altering one or more of several variables including signal rate, location of feeds, types of feeds, timing of signal, quantity of feeds energized, intensity of signal, shape of enclosure, density of plasma, and type of composition used to form the plasma, to name a few.
It is another object of the present invention to provide a single plasma antenna that may be used in the place of several conventional antennas.
These and other objects may be accomplished by the plasma antenna and methods of the present invention. The plasma antenna is comprised of a) an enclosed chamber; b) a composition contained within the enclosed chamber capable of forming a plasma; c) at least three energizing points capable of forming electromagnetic contact with the composition; and d) an energy source coupled to the at three energizing points for developing at least one conductive path of plasma within the enclosed chamber. Preferably, the plasma antenna may further comprise a modifying mechanism to reconfigure the conductive path. In the most simple embodiment, any combination of three energizing points may be energized, i.e., any single energizing point, any two energizing points, or all three energizing points.